Prior art technologies involve infrared light which has high directionality and is not usable with any interfering object. Because of the above characteristics, the prior art technologies suffer from flexibility in connection and ease of use.
In the recent years, the Bluetooth protocol has been developed to wirelessly connect peripherals or terminals. The Bluetooth protocol involves a radio wave technology to connect the peripherals and terminals without any cables. Bluetooth involves a short-distance radio wave technology that lacks strong directionality and is resilient with interfering objects. Because of the above characteristics, the Bluetooth technology is more desirable than the above described prior art infrared technology.
Furthermore, according to the Bluetooth protocol, peripheral devices and terminals are easily connected with each other any time and any where without user intervention. The Bluetooth protocol specifies 2.4 GHz for communicating at a maximal rate of 1 mega bits per second (Mbps) over up to approximately 100 meters. The following prior art includes the above described Bluetooth technology.
Japanese Patent Publication Hei 2000-276269 discloses a wireless data input device for transmitting data from a keyboard or a mouse to a plurality of computers based upon the Bluetooth protocol. A user selects a predetermined computer by a switch so that a single data input device services a plurality of the computers without cable connections and limitation to the location. No disclosure is provided with respect to the Bluetooth protocol.
Toshiba recently introduced a video conferencing system called “SPANworks 2000” based upon the Bluetooth protocol. The system includes personal computers that are each equipped with a PCMCIA card for communicating according to the Bluetooth protocol. In the Bluetooth network or piconet, a master terminal simultaneously transmits presentation image data to a plurality of slave terminals. Since the slave terminals are always active in the network and cannot be placed in a sleep mode or a low power consumption mode, a maximal number of the slave drives is limited to seven. The version 1.0B of the Bluetooth protocol limits the above maximal number of seven active slave terminals for each master terminal. Although the save Bluetooth protocol provides that the active slave terminals can be put into a park mode, an inactive state or a sleep mode in order to have more than seven slave terminals, no enabling disclosure has been provided for implementation. The park mode, the inactive state or the sleep mode are used synonymously used throughout in the current application.
For example, one implementation is for a master terminal to switch the mode of a slave terminal based upon a request from the slave terminal. Upon receiving a request from one of more than seven slave terminals that are connected to a master terminal via the piconet, the master terminal unconditionally switches a park or inactive slave mode into an active mode in the corresponding slave terminal. During a video conference, the above scheme causes the slave terminals to have significantly uneven time for data transmission. Consequently, the video conference is disturbed.
For the above described reasons, it is desired that a plurality of the slave terminals should have an efficient connection scheme in the piconet.